The key here is to notice that causal arguments in general are susceptible to alternative causes. I initially chose A because a few words matched the stimulus, but that's never a good strategy -- too myopic. Option D is better because causal arguments are inherently weak to other causes (or different relationships). To answer this correctly, one must take a step back and analyze the line of reasoning in the argument.
A. presumes, without providing justification that only highly educated people make informed choices
- Wrong because of "only"
B. overlooks the possibility that people who make informed choices may nonetheless suffer from inherited vices
- 1) Neutral. Do inherited vices cause someone to not have optimism? Don't know. 2) Tangential to the argument.
C. presumes, without providing justification, that informed choices are available to everyone
- Weaken. Reverse logic. since Informed choices is sufficient condition, and high education is necessary condition, informed choices come from those who have high education.
D. overlooks the possibility that the some factors other than genetics and culture may causally contribute both to education and to high optimism
- Correct. Classic scenario
E. does not acknowledge that some people who fail to make informed choices exude high optimism
- Neutral. If those who don't make informed decisions exude high optimism may or may not be a significant number. Since it doesn't specify, this is a non-factor.